You need to download the ebuild from the Web site to which you linked, then install it via a local overlay. I don't need (or want) to install it myself but, if you don't know how to use Portage and local overlays, the method would be something along the lines listed below. All the commands below must be done as root user (hence the hash prompt shown in the steps below). Open a Konsole/Terminal window and log in as the root user.

1. Synchronise with the Portage repositories those ebuilds on your PC that are in the Portage tree: